1. Field of the Invention
This invention relates to a delivery system for agriculturally active chemicals, and, more particularly, to a clear, one-phase, efficacious aqueous microemulsion for delivering a pyrethroid insecticide at a high loading.
2. Description of the Prior Art
Agriculturally active chemicals are most preferably applied in the form of aqueous emulsions, solutions or suspensions. Occasionally, they may also be applied in the form of a dust wherein the active ingredient is adsorbed onto or mixed with a finely divided inert carrier material, such as, china clay, or the like. With such powdered or dust compositions, drift due to wind is a problem and consequently, liquid formulations are preferred.
One of the problems with such liquid formulations is the fact that chemicals having agricultural activity often exhibit extreme insolubility in water. This results in their having to be dissolved either in organic solvents or utilized in the form of emulsions or suspensions. With respect to the use of organic solvents, these are generally disadvantageous from an environmental and cost viewpoint. Particularly, such organic chemicals may exhibit toxicity or side-effects which may be adverse to the effect of the agricultural chemical itself or to the subsequent fruit or vegetable produced in the particular agricultural use. This toxicity may also be disadvantageous with respect to handling.
When attempts are made to provide emulsified or suspension formulations, difficulties are encountered with respect to providing a desirably high concentration of the agriculturally active ingredient. Thus, when such agriculturally active chemicals are formulated into a macroemulsion (sometimes referred to herein as an emulsion), it is difficult to maintain the emulsified state. This, in turn, creates problems in maintaining a uniform formulation, particularly, when the formulation is diluted with water for application to the plants.
U.S. Pat. No. 5,317,042 disclosed a clear stable, efficacious aqueous microemulsion of a pyrethroid insecticide, alone, or in a complex mixture, obtained by mixing the insecticide with an inert matrix composition containing a defined mixture of nonionic surfactant to form a microemulsion concentrate, and diluting with water. The inert matrix composition consisted of a predetermined mixture of nonionic surfactants which also included nonylphenol ethoxylate with HLB&gt;6. However, the presence of nonylphenol ethoxylate in the formulation may be considered detrimental in some cases.
It is also desired to provide an aqueous microemulsion a pyrethroid insecticide which is free of nonylphenol ethoxylate, and which is stable upon formation, and which can be used within a relatively long time, without significant hydrolysis or precipitation.